Scoliosis, a disease that deforms the spine, affects more girls than boys and manifests itself during the teen years when significant growth is experienced. Scoliosis generally combines a horizontal torsion and flexion in a frontal plane and develops in three spatial dimensions. As noted, the disease generally begins with the growth phase, as it is hypothesized that this is probably due to the rotation of one or two vertebral bodies.
Sufferers of scoliosis are generally treated initially with a rigid corset-like orthopedic brace. If this treatment proves unsuccessful, another treatment option can include spinal fusion through invasive surgery. Spinal fusion can oftentimes largely correct a spinal deformity but can also result in complications, such as when the patient advances into adult life. Spinal fusion requires significant invasive surgery, oftentimes including the dissection of the paraspinous muscles of the vertebral body and exposure of the facet joints and laminae. Typical treatment devices include one and oftentimes two rods mounted on either side of the spinal column. If two rods are employed, anchoring means are provided for positioning the rods in spaced-apart parallel alignment. Hooks or screws are employed to anchor the rods along the selected portion of the spinal column for treatment, typically requiring relatively deep penetration of the cortical bone above one or both of the pedicles. The anchors are rigidly locked to the associated rod to prevent relative motion therebetween, and the entire arrangement can be supplemented with bone grafts.
Similar systems have been proposed to treat scoliosis without directly fusing adjacent vertebral bodies. However, because the implantation procedure is so invasive, it can lead to increased blood loss, generation of scar tissue and may induce the risk that the vertebral bodies will still fuse through reaction of the body itself, i.e., auto-fusion.
Others have suggested improvements to the orthosis described above. For example, U.S. Pat. No. 6,554,831 suggests a system that allows for may intraoperative correction and micro-movement of the vertebrae despite implantation of a corrective rod. The '831 patent teaches use of a rigid dual-rod arrangement with fixed and mobile brackets that are anchored to the transverse process and, thus, require significant invasive surgery and risk consequent fusion. The '831 patent discloses attaching a curved rod to a connector device that is, in turn, attached to a pedicle screw by way of a ball-and-socket joint for the purpose of allowing articulation between the rod and the screw. However, this configuration allows the curved rod to rotate out of alignment with the spinal column and, consequently, shifts the direction in which the corrective force is intended to be applied. Use of the ball-and-socket joint with a fixed bracket further causes the point of articulation to be undesirably offset from the rod itself.
U.S. Pat. No. 5,672,175 suggests another approach that theoretically provides a patient with close-to-normal range of motion of the vertebrae by instrumenting the spine with elastic members pre-curved to correct the spinal deformity. Anchoring to the transverse process is also employed, which, again, is a major drawback in performing the techniques suggested in the '175 patent. Further, this device theoretically overcomes the deformity with constant force applied by pre-curved correction members, but this does not allow for resultant changes in the deformity or tissue relaxation. Because of the use of these pre-curved rods, the technique suggested in the '175 patent may actually result in a final deformity completely opposite to the original deformity due to tissue growth and relaxation. Furthermore, this device risks alteration of the natural biomechanics of the spine by fixing the distance between points of attachment. This prohibits any change in distance between pedicles, which shifts the center of rotation of each affected vertebral body anteriorly.
U.S. Pat. No. 4,697,582 suggests a correction apparatus that employs an elastic rod or a pair of elastic rods exhibiting a memory shape of the corresponding part of a normal rachis, the rods being immobilized in rotation in each of the guidance openings. However, the mechanical assembly suggested in the '582 patent is appended to an area on each vertebrae between the spinal process and transverse process, which, again, results in significant invasive surgery, (as discussed earlier) and can result in fusion of vertebral bodies in the to-be corrected region.
Therefore, a spinal correction system is needed to correct spinal deformities while eliminating or significantly reducing the drawbacks of conventional systems.